A quadratic optimization method for connectivity and coverage control in backbone-based wireless networks

The use of directional wireless communications to form flexible mesh backbone networks, which provide broadband connectivity to capacity-limited wireless networks or hosts, promises to circumvent the scalability limitations of traditional homogeneous wireless networks. The main challenge in the design of directional wireless backbone (DWB) networks is to assure backbone network requirements such as coverage and connectivity in a dynamic wireless environment. This paper considers the use of mobility control, as the dynamic reposition of backbone nodes, to provide assured coverage-connectivity in dynamic environments. This paper presents a novel approach to the joint coverage-connectivity optimization problem by formulating it as a quadratic minimization problem. Quadratic cost functions for network coverage and backbone connectivity are defined in terms of the square distance between neighbor nodes, which are related to the actual energy usage of the network system. Our formulation allows the design of self-organized network systems which autonomously achieve energy minimizing configurations driven by local forces exerted on network nodes. The net force on a backbone node is defined as the negative energy gradient at the location of the backbone node. A completely distributed algorithm is presented that allows backbone nodes to adjust their positions based on information about neighbors’ position only. We present initial simulation results that show the effectiveness of our force-based mobility control algorithm to provide network configurations that optimize both network coverage and backbone connectivity in different scenarios. Our algorithm is shown to be adaptive, scalable and self-organized.     

Managerial identity work in action: performative narratives and anecdotal stories of innovation

Innovation is invariably accepted as a central component of construction sector competitiveness. Yet, there remains a paucity of empirical research, which explores the gap between the way innovation is promoted in the policy discourse and how it is interpreted in practice. We follow the “narrative turn” in organization studies to explore the ways in which senior executives in the UK construction sector ascribe themselves with informal roles while advocating the cause of innovation. Empirical data is derived from narrative interviews with 32 senior executives who self-identify as “innovation champions”. When talking about innovation, the respondents were found to oscillate between performative narratives of innovation and more personalized stories derived from their own experience. The narratives were invariably pre-rehearsed often to the point of being monotonous. In contrast, the personalized stories tended to be engaging and emotionally laden. The tendency for senior executives to oscillate between narratives and stories is seen as an important means through which they search for meaning while at the same time legitimizing their self-identities as “innovation champions”. Of particular note is the way in which senior managers self-ascribe themselves with informal roles which are notably at odds with those described in more formalized narratives.     

A MODEL FOR SIMULATING RESIDENTIAL DEVELOPMENT

This article is the outgrowth of a long period of experimentation with models of residential and other development which focus on the individual decision-maker—the householder in search of a home, and the builder attempting to cater to his desires. The first part of the paper describes the means by which this process is simulated in a computer. Later parts of the paper indicate how this view of consumer behavior has led naturally into a consideration of households' activity patterns and into research on these patterns. In conclusion the author indicates by implication that the integration of these two approaches may lead in the direction of measurements of accessibility and of taking account of the competition fm desirable sites, of consequent increases in the intensity of utilization, and of the rents of these sites. Thus this article, in conjunction with others, illustrates a remarkable convergence between research starting at the level of individual decision units and coming to consider the larger framework, and research starting from gross changes in the metropolitan configuration and coming to give increasing consideration to the actual decision process.     

Increased conversion efficiency in cadmium telluride photovoltaics by luminescent downshifting with quantum dot/poly(methyl methacrylate) films

Commercially available quantum dots have been encapsulated in a poly(methyl methacrylate) film and used as a luminescent downshifting layer on cadmium sulfide/cadmium telluride photovoltaic devices. Application of these films has resulted in a relative improvement to the short‐circuit current of over 4% by I–V measurement, with a significant increase in the contribution of short‐wavelength light resulting in 25% of the current available in this part of the spectrum being captured. The films have been shown to be highly scattering and the associated difficulties this provides to external quantum efficiency measurements have been discussed. A range of optical characterisation techniques, particularly laser beam induced current, have been used to probe the effect the films have on a cadmium sulfide/cadmium telluride device. An alternate methodology for performing external quantum efficiency measurements with the quantum dot films has been proposed. Copyright © 2013 John Wiley & Sons, Ltd.     

Analysis of equiangular spiral antennas

In this work, equiangular spiral antennas are analyzed with the well-known method of moments in conjunction with triangular patch modeling. In particular, the analysis focuses on the validity of several generic guidelines hitherto available for designing such antennas. In our study, numerical results indicate that increasing the number of spiral arm turns broadens the radiation pattern (i.e., the axial ratio increases), but that tapering the outermost portion of the arms has little effect. Furthermore, as a spiral is wrapped tighter, the radiation pattern broadens and the gain increases. We also show that the useful frequency range of the spiral antenna depends not only on the spiral arm length and the inner radius near the spiral center, but also on the wrap tightness. Finally, numerically determined input impedance differed considerably from the 188-Ω impedance expected for these self-complementary type antennas. © 1996 John Wiley & Sons, Inc.     

Effect of Coordinating Solvents on Solution Speciation and the Crystallisation via ROP of a Triphos-Silver Coordination Cage

There is a general lack of understanding of how coordination polymers (metal-organic frameworks) form. Some insight can be gained from observations of formal ROP (ring-opening polymerisation) relationships between coordination polymers and their discrete soluble precursors. Most ROP examples reported previously have involved bidentate bridging ligands. Here we present an unusual example of a ROP relationship based on a tripodal ligand. In particular, 1,3,5-tris(diphenylphosphino)benzene (L1) is found to form a symmetrical coordination cage of stoichiometry Ag₃(L1)₂ in solution in acetonitrile. This contrasts with previous observations in less-coordinating solvents in which higher nuclearity cages are also formed, and shows that the coordinating acetonitrile solvent reduces anion-templating effects. On crystallization from acetonitrile a one-dimensional polymeric structure [Ag₃(L1)₂(NCCH₃)(OTf)₃] _n is obtained. The structure is noteworthy in being a ROP isomer of the trinuclear cage observed in solution. The structure also exhibits solvent-filled channels (maximum diameter 6.1 Å) but the material is not stable to desolvation. The structure of the polymer contrasts with that obtained from less-coordinating solvents, the latter being a stable hexagonal 2-dimensional structure with nanoporosity.     

Treatment of Critical Size Femoral Bone Defects with Biomimetic Hybrid Scaffolds of 3D Plotted Calcium Phosphate Cement and Mineralized Collagen Matrix

To treat critical-size bone defects, composite materials and tissue-engineered bone grafts play important roles in bone repair materials. The purpose of this study was to investigate the bone regenerative potential of hybrid scaffolds consisting of macroporous calcium phosphate cement (CPC) and microporous mineralized collagen matrix (MCM). Hybrid scaffolds were synthetized by 3D plotting CPC and then filling with MCM (MCM-CPC group) and implanted into a 5 mm critical size femoral defect in rats. Defects left empty (control group) as well as defects treated with scaffolds made of CPC only (CPC group) and MCM only (MCM group) served as controls. Eight weeks after surgery, micro-computed tomography scans and histological analysis were performed to analyze the newly formed bone, the degree of defect healing and the activity of osteoclasts. Mechanical stability was tested by 3-point-bending of the explanted femora. Compared with the other groups, more newly formed bone was found within MCM-CPC scaffolds. The new bone tissue had a clamp-like structure which was fully connected to the hybrid scaffolds and thereby enhanced the biomechanical strength. Together, the biomimetic hybrid MCM-CPC scaffolds enhanced bone defect healing by improved osseointegration and their differentiated degradation provides spatial effects in the process of critical-bone defect healing.     

Solvent-free oxidation of benzyl alcohol using titania-supported gold–palladium catalysts: Effect of Au–Pd ratio on catalytic performance

The oxidation of benzyl alcohol with molecular oxygen under solvent-free conditions has been investigated using a range of titania-supported Au–Pd alloy catalysts to examine the effect of the Au–Pd ratio on the conversion and selectivity. The catalysts have been compared at high reaction temperature (160 °C) as well as at 100 °C, to determine the effect on selectivity since at lower reaction temperature the range of by-products that are formed are limited. Under these conditions the 2.5 wt.% Au–2.5 wt.% Pd/TiO₂ was found to be the most active catalyst, whereas the Au/TiO₂ catalyst demonstrated the highest selectivity to benzaldehyde. Toluene, formed via either a hydrogen transfer process or an oxygen transfer process, was observed as a major by-product under these forcing conditions.